This invention relates generally to electrical switches and, more particularly, to automatic transfer switches.
Many businesses use transfer switches for switching power sources, for example, from a public utility source to a private secondary supply, automatically within a matter of seconds. Critical load businesses, such as, for example, hospitals, airport radar towers, high volume data centers are dependent upon automatic transfer switches to provide continuous power. Transfer switches typically utilize a plurality of contacts that can be open or closed.
Typically, it is desired that a transfer switch remain closed during a fault or overcurrent condition. During a fault condition, a large and quick influx of electrical energy causes a blow open force between the contacts. Therefore, if not locked together, the contacts will interfere with upstream protection (i.e. circuit breakers) and upset coordination between devices. Known transfer switches incorporate a toggle locking of an external mechanism to keep the switch closed during a fault condition. However, this external locking is distant from the contacts of the switch and, accordingly, a play exists in the structure between the lock and the contacts. This play and a shaft torque allow the contacts to separate slightly during a fault condition due to the blow open force. When the contacts are separated slightly, an arcing across the contacts occurs damaging the contacts.
In one aspect, a method for locking contacts in an automatic transfer switch is provided. The automatic transfer switch includes a plurality of pole units including a plurality of contact pairs. The method includes mounting an interior locking device in at least one pole unit and locking at least one contact pair individually with the interior locking device housed in that contact pair""s pole unit.
In another aspect, a pole unit for an automatic transfer switch is provided. The pole unit includes a housing, a load lug housed in the housing, and an interior locking device mounted in the housing to electrically couple to the load lug in a first position and in a second position. The pole unit further includes a plurality of source lugs including a first source lug and a second source lug mounted in the housing, wherein each source lug is electrically isolated from each other and the load lug, and the interior locking device is configured to electrically couple at least one of the first source lug and the second source lug to the load lug.
In another aspect, an automatic transfer switch is provided. The automatic transfer switch includes a plurality of pole units including a bore therethrough, wherein the housing units are connected with the bores aligned. The switch further includes at least one interior locking device mounted in at least one of the units, the interior locking device comprising a bore therethrough, wherein the bore of the locking device is aligned with the bores of the units. The automatic transfer switch further includes an end wall comprising a bore aligned with the bores of the units and a shaft axially mounted in the interior locking device bore and the housing unit bore. The shaft extends through the end wall and includes an extended portion, and a flywheel is mounted on the extended portion of the shaft.
In a further aspect, a pole unit for an automatic transfer switch includes a housing and at least one of a dual disk and a conjugate cam mounted in the housing. The conjugate cam has a tri-lobal shape and is within a conductor assembly. The dual disk includes a driving disk and a driven disk, wherein the driving disk includes a cammed surface configured to engage at least one locking tab.